The molecular phylogeny of the white blister rust genus Pustula reveals a case of underestimated biodiversity with several undescribed species on ornamentals and crop plants.

Despite their economic importance, the knowledge of the biodiversity of many plant pathogens is still fragmentary. In this study we show that this is true also for the white blister rust genus Pustula that is parasitic on several genera in the asterids, including sunflower and the gentian, Eustoma. It is revealed that several distinct species exist in Pustula, suggesting that species are mostly host genus specific. No geographic patterns were observed in the occurrence of Pustula, the host range of which includes the Araliaceae, Asteraceae, Gentianaceae, and Goodeniaceae. Evidence points to these becoming hosts as a result of jumps from the Asteraceae, with subsequent host-specific adaptation and speciation. Among the undescribed species are pathogens of economic importance, e.g. the white blister rusts of sunflower, or with still restricted geographical ranges, e.g. Pustula centaurii, which could potentially spread with international seed trade, if no quarantine restrictions are implemented.